Projection exposure apparatuses serve to image structures for the microlithographic creation of microstructured or nanostructured components in electrical engineering or microsystems technology. In such apparatuses, various components, such as optical elements, for example mirrors or the like, but also other components, such as fastening frames, actuator elements or the like, are mounted with a degree of movability, in order to example to avoid the transmission of oscillations through rigidly mounted components. However, in the case of movably mounted components, which can also be the to be softly mounted components, it is desirable for these components to be secured against excessive movement of the movable component elements as a result of unexpected external influences or during transport.
To this end, elements referred to as stop elements, referred to as end stops or transport securing means, are known, which can limit the range of movement of the movable component elements or fix the latter. In this way, it is possible to prevent the movable component elements from moving excessively and/or to prevent the movements thereof from building up and wide-ranging movements with a high speed of movement taking place as a whole, in the case of which damage to the component elements could occur in the event of a collision with adjacent component elements.
In addition to the end stops or fixing devices, or generally movement limiting apparatuses, there are damping elements in order to be able to dissipate the kinetic energy or oscillation energy in the system. Damping elements can also be combined with the end stops or fixing elements, for example by way of an appropriate configuration of the surfaces of the end stops or of the fixing means with elastic materials, such that, in the event of contact between a movable component element and an end stop damped with an elastic material, energy can be dissipated by the elastic deformation of the elastic material.
Examples of movement limiting apparatuses in projection exposure apparatuses are described for example in the German laid-open specification DE 10 2011 087 389 A1 and the international patent application WO 2012/013559 A1.
DE 10 2011 087 389 A1 describes a variable stop for an optical element, in which the stop is configured in an adjustable manner in order to allow the optical element, the movement of which is intended to be limited by the stop, to be positioned in different positions.
WO 2012/013559 A1 describes an arrangement and a method for damping shock loads in optical systems, wherein, in addition to mechanical stops which limit the range of movement of a movably mounted component element, induction arrangements are provided which induce electrical current in the event of a movement of the element of which the movement is to be limited, such that kinetic energy can be dissipated by the induction of electrical current and conversion of the electrical current into thermal energy. To this end, the induction arrangement has a magnetic plate which is arranged on the movable optical element, and a coil arrangement which is provided on a supporting structure, relative to which the optical element moves.
In WO 2012/013559 A1, the induction arrangement is additionally used as an actuator to deform the optical element, wherein, in this case, a magnetic field is generated at the coil arrangement by application of a suitable voltage and generation of a current flow, the magnetic field either attracting or repelling the magnetic plate on the optical element, in order for example to counteract a change in shape of the optical element as a result of gravitational influences. The induction arrangement is used only in the case of transport as a transport securing means in that the coil arrangement is short-circuited via a resistor such that a movement of the magnetic plate relative to the coil arrangement induces electrical current, wherein induced current is dissipated as heat via the resistor, such that the induction arrangement with the magnetic plate can function as a damping element.
However, in WO 2012/013559 A1, only passive damping in conjunction with mechanical stop elements is proposed, and so, although the speed at which the component element of which the movement is to be limited strikes the mechanical stop elements or the forces that occur when the movable component element butts against the stop elements can be reduced, mechanical contact can nevertheless take place, and this can result in damage to the component elements involved. As a result, although WO 2012/013559 A1 already provides some improvement in limiting movement and securing movable component elements in projection exposure apparatuses, the reduction in the impact energy that is to be dissipated upon mechanical contact between the movable component element and the stop elements may be unsatisfactory.